The present invention relates to a process for preparing 1,2-diols from olefins using catalysts based on transition metal compounds.
1,2-Diols, in particular cis-1,2-diols, are of industrial importance as fine chemicals, solvents, starting materials for polyesters and other polymers, and also as intermediates for agrochemicals. Propylene glycol and ethylene glycol in particular are of extraordinary importance as bulk chemicals. Numerous 1,2-diols are also of commercial interest for the preparation of pharmaceuticals, cosmetics, cleaners and are employed in the textiles and plastics industries. In many cases, the carboxylic esters display a constant viscosity over, a wide temperature range, combined with a high boiling point. They are good synthetic lubricants and plasticizers.
A frequently employed method of synthesizing 1,2-diols in the university sector are xe2x80x9cdihydroxylation reactionsxe2x80x9d such as the Sharpless dihydroxylation reaction in which olefins are reacted in the presence of osmium tetroxide and an oxidant. Review articles which describe this methodology may be found, for example, in xe2x80x9cAsymmetric Dihydroxylation Reactionsxe2x80x9d M. Beller, K. B. Sharpless, in B. Comils, W. A. Herrmann (Eds.), VCH, 1996, Weinheim, and H. C. Kolb, M. S. Van Nieuwenhze, K. B. Sharpless, Chem. Rev. 1994, 94, 2483.
From an industrial point of view, olefins are available in virtually unlimited quantities as a source for the synthesis of diols, so that metal-catalyzed dihydroxylation reactions could in principle be used for the preparation of commercially interesting products such as propylene glycol and also fine chemicals such as 1,2-pentanediol and pinacol. Although catalytic oxidation processes are frequently superior in ecological terms to stoichiometric oxidation processes, the abovementioned products are at present produced predominantly via noncatalytic multistate processes. e.g. stoichiometric reactions with peracids or hydrogen peroxide and subsequent hydrolysis of the epoxide formed as an intermediate. This is due to the known reoxidants for manganese, ruthenium and osmium oxides being too expensive for an industrial preparation of fine and bulk chemicals and only allowing the economical preparation of extremely high-priced pharmaceutical intermediates.
The dialcohols can be synthesized stoichiometrically from olefins by reaction with KMnO4 (A. J. Fatiadi, Syntiesis 1984, 85-127; W. P. Weber, J. P. Shepard, Tetrahedron Lett. 1972; 48, 4907-4908; E. Salamci, H. Segan, Y. Sxc3xcbeyaz, M. Balci; J. Org. Chem. 1997, 62, 2453-2557; B. G. Hazra, T. P. Kumar, P. L. Joshi, Liebigs Ann. Chem. 1997, 1029-1034). RuO4 gives dialcohols by stoichiometric reaction of olefins (L. Albarella, V. Piccialli, D. Smaldone, D. Sica, J. Chem. Res. 1996, 9, 400-401) and by means of catalytic reaction using NaIO4 as reoxidant (T. K. M. Shing, E. K. W. Tam, V. W. F. Tai, I. H. F. Chung, Q. Jiang, Chem. Eur. J. 1996, 2, 50-57; T. Sugai, H. Okazaki, A. Kuboki, H. Ohta, Bull. chem. Soc. Jpn. 1997, 70, 2535-2540; J. Angermann, K. Homann, H. U. Reissig, R. Zimmer Synlett 1995, 1014-1016; M. Desjardins, L. Brammer Jr., T. Hudlicky, Carbohydrate Res. 1997, 504, 39-42; M. J. Mulvihill, M. J. Miller, Tetrahedron 1998, 54, 6625-6626). Initial work on dihydroxylation by means of osmium oxide involved stoichiometric reactions (O. Makowka, Chem. Ber. 1908, 45, 943; R. Criegee, Liebigs Ann. Chem. 1936, 522, 75; R. Criegee, Angew. Chem. 1937, 50, 153). Reactions using catalytic amounts of osmium tetroxide and chlorates as reoxidants (K. A. Hoffmann, Chem. 1912, 45, 3329) or H2O2 in tert-butanol (N. A. Milas, J. H. Trepagnier, J. T. Nolan, M. Ji. Iliopolus, J. Am. Chem. Soc. 1959, 81, 4730) as reoxidant lead to overoxidation of the diols formed. Use of H2O2 results in formation of peroxoosmic acid H2O2O6 which cleaves the diol formed as an intermediate and leads to carbonyl compounds. To reduce the overoxidation, tert-butyl hydroperoxide in the presence of Et4NOH (K. B. Sharpless, K. Akashi, J. Am. Chem. Soc. 1976, 98, 1986; P. H. J. Carlsen, T. Katsuki, V. S. Martin, K. B. Sharpless, J. Org. Chem. 1981, 46, 3936; F. X. Webster, J. Rivas-Enterrios, R. M. Silverstein, J. Org. Chem. 1987, 52, 689; V. S. Martin, M. T. Nunez, C. E. Tonn, Tetrahedron Lett. 1988, 29, 2701; M. Caron, P. R. Carlier, K. B. Sharpless. J. Org. Chem. 1988. 53. 5185). tertiary amine oxides and in most cases N-methylmorpholine N-oxide (NMO: Upjohn Process) (W. P. Schneider. A. V. McIntosh, U.S. Pat. No. 2,769,824 (1956); V. Van Rheenen, R. C. Kelly, D. Y. Cha, Tetrahedron Lett. 1976, 17, 1973) are used as reoxidants. Trimethylamine oxide is superior to NMO for trisubstituted and sometimes also tetrasubstituted alkenes (R. Ray, D. S. Matteson, Tetrahedron Lett. 1980, 21, 449). Despite the selective and catalytic dihydroxylation which is possible using N-oxides, the price of these reoxidants is prohibitive for relatively large-scale industrial applications.
In recent years, Na3[Fe(CN)6] in the presence of sodium carbonate in a 2-phase system has been used very successfully as reoxidant for OsO4 (M. Minato, K. Yamamoto, J. Tsuji, J. Org. Chem. 1990, 55, 766; M. P. Singh, H. S. Singh, B. S. Arya, A. K. Singh, A. K. Sisodia, Indian J. Chem. 1975, 13, 112), particularly also in enantioselective dihydroxylation (Y. Ogino, H. Chem, H. L. Kwong, K. B. Sharpless, Tetrahedron Lett. 1991, 32, 3965). Significant disadvantages for the synthesis of the diols on a relatively large scale are again the price and the superstoichiometric amount of iron complex to be used (3 mol=990 g per 1 mol of substrate) with addition of potassium carbonate (3 mol=420 g). In the case of processes for the electrochemical oxidation of the Na4[Fe(CN)6] formed in the reaction to give Na3[Fe(CN)6] (Sepracor Inc. (Y. Gao, C. M. Zepp), PCT Int. Appl. WO 9 317 150, 1994; Anon., Chem. Eng. News. 1994, 72 (24), 41), too, industrial implementation is difficult since electrochemical processes are generally too expensive because of the apparatus required.
To circumvent the disadvantages of the abovementioned reoxidants, attempts have been made in the past to use air or oxygen for the reoxidation of OsVI to OsVIII. Such a process is the most attractive method from economic and ecological points of view. However, Cairns et al. have shown that no 1,2-dialcohol is observed in the reaction of allyl alcohol, ethylene, cyclohexene and styrene in the presence of OsO4 and oxygen, but in all cases overoxidation results in formation of industrially unusable amounts of the corresponding carboxylic acids, e.g. benzoic acid (styrene as substrate) and CO2 (J. F. Cairns. H. L. Roberts. J Chem. Soc. (C) 1968. 6-401. In a process of Celanese Corporation (GB-B 1.028.940). too, only formic acid and heptanoic acid are obtained from 1-octene. Even in the reaction of the less oxidation-sensitive ethylene, the 1,2-diol is obtained only in traces (2% of glycol after 4 hours at an O2-pressure of 7 MPa). Employees of Exxon utilize bimetallic systems comprising OsO4 and Cu(II) salts (U.S. Pat. No. 4,496,779, EP-B 0 077 201, R. G. Austin, R. C. Michaelson, R. S. Myers in Catalysis in Organic Ractions (Ed: R. L. Augustine), Marcel Dekker, New York 1985, p. 269). In a manner analogous to the Wacker process, OsVI is reoxidized by the Cu salt which is then oxidized again by means of O2. In this process, maximum conversions of propylene are 3-5% after a reaction time of 2 hours and a pressure of 28 bar.
In summary, it can be seen that the known methods for reoxidizing osmium, ruthenium and manganese by means of molecular oxygen are not usable in dihydroxylation reactions for synthesizing dialcohols.
To avoid the abovementioned disadvantages of the known catalytic processes, it is an object of the invention to develop a novel process for metal-catalyzed dihydroxylation which is simple to carry out and gives 1,2-diols in high yield and purity, with molecular oxygen being used as reoxidant, and is suitable for industrial implementation.
This object is achieved by a process for the dihydroxylation of olefins by means of transition metal catalysts in which, according to the invention, monofunctional, bifunctional and polyfunctional 1,2-diols of the formula I,
R1R2C(OH)xe2x80x94C(OH)R3R4xe2x80x83xe2x80x83(I)
where
R1 to R4 are each, independently of one another, hydrogen, alkyl, CN, COOH, COO-alkyl, COO-aryl, CO-alkyl, CO-aryl, O-alkyl, O-aryl, O-CO-aryl, O-CO-alkyl, OCOO-alkyl, N-alkyl2, NH-alkyl, N-aryl2, NH-aryl, NO, NO2, NOH, aryl, fluorine, chlorine, bromine, iodine, NO2, Si-alkyl3, CHO, SO3H, SO3-alkyl, SO2-alkyl, SO-alkyl, CF3, NHCO-alkyl, CONH2, CONH-alkyl, NHCOH, NHCOO-alkyl, CHCHCO2-alkyl, CHCHCO2H, PO-(aryl)2, PO-(alkyl)2, PO3H2, PO(O-alkyl)2, where alkyl represents an aliphatic organic group having from 1 to 18 carbon atoms which may be linear, branched and/or cyclic and aryl is a 5-, 6- or 7-membered aromatic ring which contains from 4 to 14 carbon atoms and may be fused and contain from 0 to 3 heteroatoms such as N, O, S and where the alkyl and/or the aryl group may bear up to six further substituents selected independently from among hydrogen, alkyl, O-alkyl, OCO-alkyl, O-aryl, aryl, fluorine, chlorine, bromine, iodine, OH, NO2, NO, Si-alkyl3, CN, COOH, CHO, SO3H, NH2, NH-alkyl, N-alkyl2, PO-alkyl2, SO2-alkyl, SO-alkyl, CF3, NHCO-alkyl, COO-alkyl, CONH2, CO-alkyl, NHCOH, NHCOO-alkyl, CO-aryl, COO-aryl, PO-aryl2, PO3H2, PO(O-alkyl)2, SO3-alkyl, where alkyl and aryl are as defined above,
are obtained by reacting olefins of the formula II
R1R2Cxe2x95x90CR3R4xe2x80x83xe2x80x83(II)
where
R1 to R4 are as defined above, with molecular oxygen in the presence of an osmium, ruthenium or manganese compound or a mixture thereof in water or a water-containing solvent mixture at a pH of from 7.5 to 13.
In particular, compounds of the formula I are prepared using olefins of the formula II in which the substituents R1 to R4 are each, independently of one another, hydrogen, alkyl, CN, COOH, COO-alkyl, COO-aryl, CO-alkyl, CO-aryl, O-alkyl, O-aryl, N-alkyl2, aryl, fluorine, chlorine, bromine, iodine, CHO, CF3, NHCO-alkyl, CONH2, CONH-alkyl, NHCOO-alkyl. Here, alkyl and aryl are as defined above.
Particular preference is given to a process in which diols of the formula I in which R1 to R4 are each, independently of one another, hydrogen, alkyl, CN, COOH, COO-alkyl, CO-alkyl, CO-aryl, O-alkyl, O-aryl, aryl, fluorine, chlorine, bromine, CHO, NHCO-alkyl, are prepared. Here, alkyl and aryl are as defined above.
The process of the invention is carried out in the presence of water. It has been found to be advantageous to add a further organic solvent in addition to the olefin, The process of the invention can, in the case of various olefins, also be carried out in an olefin-water mixture without further solvent. Further solvents used are generally inert organic solvents. Suitable solvents are aliphatic ethers, aromatic or aliphatic hydrocarbons, alcohols and esters, halogenated hydrocarbons, dipolar aprotic solvents such as dialkyl sulfoxides, N,N-dialkylamides of aliphatic carboxylic acids and also mixtures thereof. Preference is given to alcohols, esters and ethers. As aqueous phase, use is generally made of a basic aqueous solution having a pH of from 7.5 to 13. The basic pH of the solution is achieved by addition of a base to the water. It is generally advantageous to carry out the reaction in buffered aqueous solutions, preferably having a pH of from 8 to 13. The buffered solution is prepared by addition of known buffers to water.
To enable the diol products to be separated off readily, it is sometimes advantageous to use an aqueous salt solution or a buffered aqueous salt solution, for example an aqueous solution of an alkali metal halide or alkaline earth metal halide, as solvent in place of water or buffered aqueous solutions.
In the process of the invention, molecular oxygen or a gas mixture comprising molecular oxygen is used as oxidant. Preference is given to gas mixtures comprising at least 15% by volume of oxygen. Particular preference is given to air and oxygen gas having an oxygen content of  less than 95%.
The reaction preferably proceeds at temperatures of from 20 to 200xc2x0 C. in many cases, it has been found to be useful to employ temperatures of from 30 to 150xc2x0 C. preferably from 40 to 100xc2x0 C. The process of the invention can be carried out under atmospheric pressure, e.g. by passing oxygen through the reaction solution. However, the reaction rate is increased when a superatmospheric oxygen pressure is employed. The process can be carried out at pressures of up to 200 bar, but is usually carried out at a pressure of up to 60 bar and preferably in the range from atmospheric pressure to 20 bar.
To achieve selectivity of the dihydroxylation reaction, the catalyst is activated by addition of an amine. Amines suitable for this purpose are, in particular, tertiary amines such as trialkylamines, dialkylarylamines, alkyldiarylamines, which may be cyclic and/or linear, pyridines and quinolones. Preference is given to bicyclic amines such as 1,4-diazabicyclo[2,2,2]octane and also compounds of the quinuclidine type and substituted phthalazines, diphenylpyrimidines and carbamoylindolines.
The transition metal catalysts used are generally oxides of the elements osmium, manganese and ruthenium, preferably osmium. These metals are generally used in oxidation states of  greater than +4. However, it is also possible to use catalyst precursors in lower oxidation states. Thee are converted under the reaction conditions into the catalytically active Os(VIII) and Os(VI) species or Mn(VII) or Ru(VIII) species. Examples of osmium catalysts or catalyst precursors which can be used are: OsO4, K2Os2(OH)4, Na2Os2(OH)4, OS3(CO)12, OsCl3, H2OsCl6, [CF3SO3Os(NH3)5](O3SCF3)2, OsO4 on vinylpyridine, ButNOsO3. Examples manganese catalysts or catalyst precursors which can be used are: MnO2, KMnO4, Ca(MnO4)2, MnCl3, Mn(OAc)3. Examples of ruthenium catalysts or catalyst precursors which can be used are: RuCl3, RuO4, RuO2.
In the process of the invention, the catalyst is used in catalytic amounts relative to the olefin. In general, use is made of from 0.2 to 0.00001 equivalents, based on olefin, preferably from 0.1 to 0.0001 equivalents and particularly preferably from 0.1 to 0.0005 equivalents. The ratio of amine to metal is from 0.01:1 to 1.000:1 preferably from 0.1:1 to 100:1. Particular preference is given to using ratios of amine to osmium of from 1:1 to 50:1.
When using bulky olefins, in particular trisubstituted and tetrasubstituted olefins, it is sometimes advantageous to add a cocatalyst to hydrolyze the metal ester formed as an intermediate. This cocatalyst is an amide which aids hydrolysis, for example a sulfonamide or/and carboxamide. Particular preference is given to the addition of methylsulfonamide.
The cocatalyst is used in an amount of from 0.01 mol% to 10 mol% (based on olefin), preferably from 0.1 to 5 mol%.
The particular advantage of the process of the invention is the use of oxygen or oxygen-containing gases as reoxidant. Despite the comparatively difficult reoxidation process, high catalyst productivities can be achieved by mixing the aqueous catalyst phase which has been used once with olefin again. In this way, the catalyst costs for the process of the invention are minimized, so that even industrial processes can be carried out economically.
The process of the invention is particularly surprising and novel since no catalyzed, selective dihydroxylation reactions to form 1,2-diols using oxygen as reoxidant have been described in the past. This is attributable to the few previous studies using oxygen as reoxidant leading essentially to overoxidation, if any reaction at all occurred. The novel combination described in the process of the invention of addition of a ligand which accelerates the dihdyroxylation and carrying out the process in a buffered basic solution surprisingly leads to a chemoselective dihydroxylation process even in the presence of oxygen. The process of the invention shows for the first time that the statements in the known literature on the catalyzed dihydroxylation using oxygen are wrong.
The particular advantages of the novel process are the price advantage of the oxidant, the simple way in which the process can be carried out and the high selectivity of the process compared with other oxidants which have been employed.
The 1,2-diols prepared according to the invention can be used, inter alia, as solvents, starting materials for polyesters and other polymers, intermediates for agrochemicals, cosmetics, cleaners and are employed in the form of their esters as synthetic lubricants and plasticizers.